The present invention relates generally to positioning systems for automated irrigation systems. In particular, the present invention relates to an improved position sensing system in a center pivot irrigation system.
Knowing (or being able to calculate) the position of each spray head along the conduit assembly of a center pivot irrigation (xe2x80x9cCPIxe2x80x9d) system is important for the precision delivery of water, fertilizer, herbicides, and pesticides. In fact, systems that control the delivery of liquids along the length (or conduit assembly) of the CPI system can require an accuracy of 3 meters or better to be effective.
Present methods of determining spray head positions such as by tracking the end of the conduit assembly include the, for example, the use of a flux-gate magnetic compass to derive angular bearing and by knowing the distance from the center to end allows the position at all points along the irrigation system to be known. Unfortunately, however, errors in the magnetic compass can exceed the system tolerances because electric current used to drive the wheel motors can cause errors in compass measurements and require expensive calibration at installation.
Another technique involves using a wheel counter that measures the rotations of a wheel located at the end of the pivot. Unfortunately, with this technique, the wheel location system can suffer from a build up of errors due to slippage and mud buildup causing an apparent wheel diameter error.
Accordingly, what is needed is an improved positioning system and method for irrigation systems including center pivot irrigation systems.
The present invention provides an improved positioning system by using differential global positioning system (xe2x80x9cDGPSxe2x80x9d) methods to monitor (or track) the absolute and/or relative position of a selected location on the conduit assembly referenced from the fixed, known position of a central tower. In one embodiment, a first global positioning system (xe2x80x9cGPSxe2x80x9d) receiver mounted at the fixed tower generates differential correction information and provides this correction information via wire or otherwise to a second GPS receiver mounted at a selected location on the conduit assembly of the irrigation assembly.
In another more particular embodiment of the present invention, the positioning system is made up of two GPS receivers, the first of which is programmed to generate differential corrections and is installed at the center of a pivot irrigation assembly, where it does not move. The second GPS receiver is installed at or near the moving end of the pivot irrigation assembly and is connected by twisted shielded wire to the first GPS receiver. The second GPS receiver receives the differential corrections from the first GPS receiver over the wire and generates corrected GPS position information. The position information enters a microprocessor system where distance and bearing are computed, averaged and reported, e.g., once every 30 seconds, to a central, controller for the irrigation system.